daiku,

Ahhh, Doug-Fir pitch...I know the stuff well.

What kind of finish already exists on the frame? Also, is the frame dripping with gooey pitch, or is it the little pinhead weeping things?

Turpentine may be another organic solvent that will do the job effectively without causeing too much harm to the finish.

Better smelling would be those citrus based oils (lemon, orange) which would probably add to the patina of the finish. Might require a little more elbow grease.

Also, they might try a heat gun or hair dryer to speed up the process and then scrape off once it cools.

Good luck.

-srj